Field of the Invention
The invention relates to a device for discharging blowing air with two pipe sections of which one is adjustably inserted into the other; the pipe sections communicate with a blowing air source on the one hand and with a blowing air discharge nozzle on the other hand; the blowing air discharge outlet is moveable in the longitudinal direction of the pipe sections by means of a relative adjustment thereof.
Feeders of sheet-fed printing machines of Heidelberger Druckmaschinen AG, for instance, are provided with devices of that kind. They serve to pre-loosen an uppermost layer of sheets to be printed and which are stacked in the feeder. A first pipe section carrying the blowing air outlet is thereby adjustable relative to a second pipe section in a telescoping fashion and the longitudinal direction of the pipe section is perpendicularly oriented, so that, in the case the device is mounted in a stationary position, the location of the blowing air outlet may be adjusted to match the level of the uppermost layer of the sheets within certain boundaries. For the purpose of allowing the aforementioned telescoping adjustment, an end piece of the first pipe section is fit into an end piece of the second pipe section and it is provided with an entrainer pin inserted transversely to its longitudinal direction whose respective ends are guided in a respective longitudinal slit of the second pipe section. The ends of the pin radially project beyond the second pipe section. The second pipe section is provided with an outer thread for a set nut cooperating therewith, on which the ends of the entrainer pin rest under the action of a spring.
The blowing air discharge outlet of the known device is defined by an array of relatively fine air discharge bores. A "soft" blowing air jet can be attained with great suitability for the aforementioned utilization for loosening an uppermost layer of sheets which are stacked in a feeder. This, however, requires a sensitive fine adjustment of the height level of the blowing air discharge outlet formed by the individual air discharge bores with respect to the height of the upper edge of the sheet stack. This fine adjustment is effected by a corresponding rotation of the above-mentioned set nut and, while it is easy to manipulate, it still entails a certain structural expense for the mechanics of adjusting the first pipe section which communicates with the blowing air discharge outlet.